Respirators are commonly worn over the breathing passages of a person for at least one of two common purposes: (1) to prevent impurities or contaminants from entering the wearer's breathing track; and (2) to protect other persons or things from being exposed to pathogens and other contaminants exhaled by the wearer. In the first situation, the respirator is worn in an environment where the air contains particles that are harmful to the wearer, for example, in an auto body shop. In the second situation, the respirator is worn in an environment where there is risk of contamination to other persons or things, for example, in an operating room or clean room.
Some respirators are categorized as being “filtering face-pieces” because the mask body itself functions as the filtering mechanism. Unlike respirators that use rubber or elastomeric mask bodies in conjunction with attachable filter cartridges (see, e.g., U.S. Patent RE39,493 to Yuschak et al.) or insert-molded filter elements (see, e.g., U.S. Pat. No. 4,790,306 to Braun), filtering face-piece respirators have the filter media comprise much of the whole mask body so that there is no need for installing or replacing a filter cartridge. As such, filtering face-piece respirators are relatively light in weight and easy to use.
Filtering face-piece respirators generally fall into one of two categories, namely, fold-flat respirators and shaped respirators. Fold-flat respirators are stored flat but include seams, pleats, and/or folds that allow the mask to be opened into a cup-shaped configuration for use. Examples of flat-fold filtering face-piece respirators are shown in U.S. Pat. Nos. 6,568,392 and 6,484,722 to Bostock et al. and U.S. Pat. No. 6,394,090 to Chen.
Shaped respirators, in contrast, are more-or-less permanently formed into a desired face-fitting configuration and generally retain that configuration during storage and use. Shaped filtering face-piece respirators regularly include a molded supporting shell structure, generally referred to as a “shaping layer”, which is commonly made from thermally bonding fibers or an open-work plastic mesh. The shaping layer is primarily designed to provide support for a filtration layer. Relative to the filtration layer, the shaping layer may reside on an inner portion of the mask (adjacent to the face of the wearer), or it may reside on an outer portion of the mask, or on both inner and outer portions. Examples of patents that disclose shaping layers to support filtration layers include U.S. Pat. No. 4,536,440 to Berg, U.S. Pat. No. 4,807,619 to Dyrud et al., and U.S. Pat. No. 4,850,347 to Skov.
In constructing a mask body for a shaped respirator, the filtration layer is typically juxtaposed against a shaping layer, and the assembled layers are subjected to a molding operation by, placing the assembled layers between heated male and female mold parts (see, for example, U.S. Pat. No. 4,536,440 to Berg) or by passing the layers in superimposed relation through a heating stage and thereafter cold molding the superimposed layers into the shape of a face mask (see U.S. Pat. No. 5,307,796 to Kronzer et al. and U.S. Pat. No. 4,850,347 to Skov).
In known shaped filtering face-piece respirators, the filtration layer—whether assembled into the mask body by either of the above-noted techniques—typically becomes attached to the shaping layer by entanglement of the fibers at the interface between the layers or by binding of the fibers to the shaping layer. Alternatively, the filtration layer may be bonded to the shaping layer shell across its entire inner surface through use of an appropriate adhesive—see U.S. Pat. Nos. 6,923,182 and 6,041,782 to Angadjivand et al. Known filtering face-piece respirators also may be welded at the periphery of the mask body to join the assembled layers together.